The present invention relates to magnetoresistance-effect element having a prominent magnetoresistance effect, a magnetoresistance-effect magnetic head incorporating this element, and a method of manufacturing the magnetoresistance-effect element.
Magnetoresistance-effect magnetic heads (hereinafter referred to as “MR heads”) that incorporate a magnetoresistance-effect element (hereinafter referred to as “MR element”) have been in common use. Each magnetoresistance-effect magnetic head utilizes the magnetoresistance effect of the MR element, thereby to read signals recorded on magnetic recording media.
An MR element is a kind of a resistance element. Its electric resistance changes as the external magnetic field changes. An MR head has an MR element, whose electric resistance changes with the signal magnetic field emanating from a magnetic recording medium. Utilizing the change in the electric resistance of the MR element, the MR head reads the signals magnetically recorded on the magnetic recording medium.
In recent years, there has been a demand for a magnetic recording medium that is small and has yet a large storage capacity. To meet this demand, the recording density of magnetic recording media is increased by, for example, narrowing the recording tracks.
On the other hand, MR heads have been improved in order to prevent a decrease in the output signal level that may result from the narrowing of the recording tracks of the media. A notable improvement is the use of an MR thin film having giant magneto-resistivity (GMR) in place of the conventional MR film having anisotropic magneto-resistivity (AMR).
Various MR films exhibiting giant magneto-resistivity are known. Of these MR films, the spin-valve film comprises an anti-ferromagnetic layer, two ferromagnetic layers and a nonmagnetic layer. The nonmagnetic layer is interposed between the two ferromagnetic layers, and the anti-ferromagnetic layer contacts one of the ferromagnetic layer. The ferromagnetic layer contacting the anti-ferromagnetic layer works as a pinned layer. The other ferromagnetic layer functions as a magnetism-sensing layer known as “free layer.” The magnetization of the free layer depends on the external magnetic field. The external magnetic field is detected from the different directions in which the pinned layer and free layer are magnetized.
In order to promote changes in the magnetoresistance of the spin-valve film, electrons may be mirror-reflected in the spin-valve film to raise the probability that the electrons scatter themselves depending on their spins.
A spin-valve film is disclosed in, for example, Jpn. Pat. Appln. Laid-Open Publication No. 11-168250 and W. F. Egelhoff et al. (J. Appl. Phys. 82 (12), Dec. 15, 1997. The spin-valve film has an anti-ferromagnetic layer that is made of an oxide. This layer causes mirror reflection of electrons. However, an anti-ferromagnetic layer made of an oxide assumes but insufficient switched connection with the ferromagnetic a ferromagnetic layer that functions as pinned layer. Further, the layer exhibits a lower thermal stability than an anti-ferromagnetic layer made of ordered-form metal and is therefore less reliable.
In order to cause mirror reflection of electrons in a spin-valve film having a commonly used anti-ferromagnetic layer, the magnetic layer that functions as free layer may be oxidized to have a smooth interface, and the smooth interface may be used to cause mirror reflection of electrons. Once oxidized, however, the free layer attains a coercive force and loses soft magnetic property. Consequently, the free layer becomes less sensitive to external magnetic fields.
The rate of changing the magnetoresistance of the spin-valve film may be promoted while preserving the soft magnetic property of the free layer. To this end, an additional layer that causes mirror reflection of electrons may be used. The interface between any two layers mounted one upon the other is rough in terms of an angstrom level. It is quite probable that the spin direction of each electron change as the electron passes through this interface. This lowers the rate of changing the magnetoresistance of the spin-valve film. That is, the additional layer reduces the rate of changing the magnetoresistance of the spin-valve film. Thus, the magnetoresistance of the spin-valve film cannot be changed as much as is expected from the mirror reflection of electrons.